A fuel tank of the type typically mounted in a vehicle, is subject to varying pressure owing to several changing parameters, e.g. fuel consumption during operation of the engine (resulting in pressure decrease within the fuel tank), temperature fluctuations (temperature increase results in pressure increase within the fuel tank whilst temperature decrease results in pressure drop within the fuel tank), refueling (resulting in pressure increase within the tank), etc.
Such pressure changes within the fuel tank may have an overall effect on the engine's performance owing to unsteady fuel supply to the engine and, in some extreme cases, may result in deformation of the fuel tank and even damage thereto, e.g. in the form of cracks which may in turn cause fuel leakage.
In modern vehicles there is typically provided a vapor control system wherein the fuel vapor is transferred from the fuel tank to a recovery device such as a carbon canister, as known per se. For that purpose, it is also known to provide a control pressure valve being in flow communication between the fuel tank and the vapor recovery device for selectively evacuating fuel vapor from the fuel tank on the one hand, and on the other hand, to allow air flow into the fuel tank. However, it is desired not to evacuate unnecessary fuel vapors from the fuel tank so as to prevent fuel droplets from flowing towards the vapor recovery system and in order to reduce fuel consumption.
Some vapor control valves are pressure responsive whereby they open or close responsive to pressure condition at the filling pipe inlet. Other pressure responsive valves respond to vapor pressure within the fuel tank itself. Still another type of fuel vapor control valves respond to the fuel level within the fuel tank.
Fuel vapor developing within the fuel tank is collected and transferred to the vapor recovery device (i.e. a carbon canister) in which air supplied to the engine is enriched by the fuel vapor for enriching the gas mixture injected to the engine on the one hand and, on the other hand, reducing or eliminating fuel vapor escaping to the atmosphere, as this is becoming an ever-growing environmental requirement and which within a few years will become a compulsory requirement by environment control authorities.
However, in order to reduce the evacuation of fuel vapor from the tank (often carrying with it also fuel droplets) and thus reducing overall fuel consumption, it is required that evacuation of fuel vapor to the carbon canister shall take place only upon increase of fuel vapor pressure within the fuel tank over a predetermined pressure threshold.
Among the prior art disclosed in this matter there is WO0208597A1 to Raval, directed to a fuel vapor pressure control valve comprising a housing fitted with a first port connectable to a fuel tank and a second port connectable to a fuel vapor recovery device, a valve assembly for admitting vapor flow in a first direction from said first port to said second port when pressure within the tank rises to a first threshold, or for admitting vapor flow in a second, opposite direction when pressure within the tank drops below the pressure at the fuel vapor recovery device.
U.S. Pat. No. 3,616,783 to Borg-Warner Corp. Discloses a multifunction valve for controlling vapor from a fuel tank, design to open at a first pressure permitting vapor flow towards a vapor collecting apparatus and remains open until the pressure has dropped to a second lower pressure, with a check valve provided to compensate for negative pressure or lowering of fuel level, and a safety relief valve is provided to protect the tank and system from excessive pressure.
U.S. Pat. No. 6,003,499 Stant Manufacturing Inc. discloses an apparatus is provided for controlling venting of vapor to and from a fuel tank. The apparatus includes a housing and first and second valves positioned in the housing. The first valve controls the primary flow of vapors from the fuel tank and includes an aperture permitting an auxiliary flow of vapor to and from the fuel tank. The second valve controls the auxiliary flow of vapor to the fuel tank and includes first and second apertures permitting vapor to flow to the fuel tank. The second valve moves between a first position permitting vapor to flow through the first aperture and a second position permitting vapor to flow through the first and second apertures at a greater flow rate.